Hyperventilating at 110 feet

[TSandM]

Actually, you can have elevated CO2 without low O2. It's the classic intern error of putting someone who is dependent on hypoxic drive onto O2 . . . you raise the oxygen in the arterial blood and the patient stops breathing, or drops their breathing to where CO2 goes through the roof.

In scuba divers, the likelihood of exerting oneself to the point of dropping arterial pO2 is low, in part because the FIO2 is so high, and also because it's almost impossible to reach those extremely high aerobic workloads because the work of breathing just won't let you do it.

But you're right -- the precise mechanism is something we can debate (and, of course, I'm right, because I'm a doctor ), but the important take home message to the diving community is that it is not a good idea to overexert yourself on scuba, and if you start to feel short of breath and panicky, do what your OW manual told you to do -- stop, hold onto something if necessary, take slow, deep breaths, and relax.

 

[Jim Lapenta]

Biggest items I see here are the following:
1. Do not trust a DM to stick to a dive plan, plan a dive, or keep you safe. In fact rely on them only for a site briefing. Then plan your own dive and stick to that.
2. Know your gear. Know what each knob, switch, button, etc. does and your use of it should be instinctual.
3. If you are going to dive with a buddy, do it. And make sure they do it or end the dive, treat it as a solo dive, or dive solo from the outset.
4. If doing the latter make sure you have the skills, knowledge, experience, equipment, and (if necessary) training to do that.
5. Did I say never trust a DM to plan a dive or keep you safe?

 

[Agility]

in part because the FIO2 is so high

Sorry to take this off topic, but IIRC the FiO2 in OC diving is determined by the gas in the tank (0.21 in case of air) and does not change during the dive (without a gas switch) wheras the ppO2 certainly rises on descent.

 

[danvolker]

I have to take issue with this (and, btw, I'm a physician with substantial critical care training).

We DO have a mechanism for sensing low arterial oxygen tension, but it is weak and poor, and nowhere near as powerful as the drive to keep CO2 down. Freedivers DO hyperventilate to get rid of CO2 before diving, but they don't do so they can "wait for the low arterial pO2 to stimulate them to breathe". They do it so they can avoid the CO2 limiting their time underwater, and the DANGER of it is that they will pass out, because they DON'T have warning from the low arterial pO2 to tell them it is going to happen.

Rapid breathing does not necessarily result in CO2 retention, but rapid SHALLOW breathing absolutely will. This is because the ventilation with shallow breaths is largely confined to exchanging the gas in the large air spaces, which do not participate in gas transfer to the bloodstream. On Scuba, if you breathe very rapidly, you will almost of necessity be breathing shallowly -- this is because the work of breathing is higher through a regulator than it is sitting in a room. The body tolerates increased work of breathing poorly. We are designed for breathing to be almost effortless, and when it isn't the person gets acutely uncomfortable. I would suspect anybody who has used a snorkel has had the experience of trying to chase some critter and getting very out of breath . . . this is because the snorkel increases dead space, and to maintain the same level of exertion as on land, one has to move much more air, and the work of breathing is very unpleasant.

Exerting yourself excessively on scuba will almost certainly result in CO2 retention. CO2 retention makes you feel anxious, and makes you breathe harder . . . and on a regulator, that translated very quickly breathing faster, but not as deep, which results in even MORE CO2 retention.

CO2 is the issue here. Remember that the air you are breathing at 4 ATA has as high an oxygen content as breathing through a high-flow mask of pure oxygen. It is difficult to get hypoxemic at depth, unless you are using a rebreather and not delivering oxygen into your breathing gas.

Another awsome post by Lynne....

I would just add that the problem of getting rid of CO2 get much worse the deeper you go....If the OP had tried swimming hard at 15 feet deep, he may not have had problems with the CO2 level, but by the time you are at 80 feet and headed for 110, CO2 Retention really changes what "any" of us can do.... An aerobic athlete may still go much faster than a non-athlete, but the aerobic athlete will not be able to work as hard at 100 feet as they can at 15 or 20 feet deep.

I am thinking the OP may have had shallow dives were he has worked hard before, but probably no deep dives where he had tried this.... He got the CO2 retention, this increased the narcotic effect of the nitrogen, and all of this could have been avoided by him having been aware of :

• You dont work hard on deep dives
• You don't follow moronic Dive Leaders or Dive Masters, that are swimming at a pace too fast for you..... Signal if possible, and if you can't get their attention, then follow whatever plan you have for separation from the leader.

 

[TONY CHANEY]

Actually, you can have elevated CO2 without low O2. It's the classic intern error of putting someone who is dependent on hypoxic drive onto O2 . . . you raise the oxygen in the arterial blood and the patient stops breathing, or drops their breathing to where CO2 goes through the roof.

Thanks for your reply. I really hope that you are not the one telling Respiratory Therapist to not give the patient too much oxygen because it will knock out their drive to breathe. If it does, and I have only seen one patient do this in 12 years, then you intubate them or use NIV because that is where they were going anyway. Now I need to get a job with the NFL so that when a runner runs the ball all the way back, instead of them grabbing the oxygen mask, I'll just put them on BiPAP or intubate them to blow off the CO2. I think that someone might build up CO2 working their butt off in high flow like Ginnie, running a reel and carrying three tanks to the lips from the eye but not very likely in this case considering the OP stated that he is very fit. Again...just my take on the situation.

 

[danvolker]

A football player or Track Sprinter or Cyclist finishing a time Trial can run to 100% max heart rate, stay their for too long, and then get tunnel vision, see spots, and everything starts shutting down. It is not a great feeling, but an athlete puts up with this....and after a couple of minutes they are fine again...One, because they are highly fit, and two, because they are on-land.
Underwater would be dangerous because of the "uncontrollable breathing" and potential for a break down of any thing but the simplest motor skills.... I as a cyclist doing 40 K time trials, this was something I became familiar with

The near panic--or just helpless maximum breathing period , this 100% heart rate held for too long can induce, would be worthwhile to describe as either too much CO2, Insufficient O2, both, or a physiological reaction to a heart rate that has run so high, for a sufficient duration that many bodily systems ( enzyme systems, etc) can begin shutting down.... Lactic acid levels are shutting down muscles and making the person nauseous as the blood lactate reaches the stomach....
Thoughts Lynne ?


P.S.

I sincerely doubt a diver would ever come close to even 85% of max HR unless on the surface in an emergency swim..

 

[TSandM]

Agility, you are of course right; I was misusing the term to make the point that you are breathing a concentration of oxygen at 4 ata that's equivalent to 80% on land -- therefore you are very unlikely to become hypoxemic.

Mr. Chaney, of course cells turn to anaerobic metabolism when metabolic demand exceeds oxygen delivery. But that's not a function of low ppO2 in the pulmonary vasculature -- it's a function of total oxygen delivery, which is limited by cardiac output and blood hemoglobin levels, assuming your hemoglobin is fully saturated -- which it will be, breathing compressed gas, as long as that compressed gas started with at least 21% oxygen. As you know, you can boost the total oxygen content in arterial blood very little by boosting the FIO2, assuming normal lungs. Oxygen is so poorly soluble in plasma that you get little benefit from it. I wish it weren't so; I've seen a couple of Jehovah's Witnesses die slow deaths because they were simply too anemic to power their tissues, despite being intubated, paralyzed, on 100% O2 and PEEP.

On land, CO2 retention simply isn't an issue, if you have normal lungs, because the work of breathing is so low. But it doesn't take a great deal of increase in WOB to make people uncomfortable. And when you try to sustain heavy exertion with increased WOB, it just doesn't work very well. At that point, minute ventilation is compromised by WOB, and CO2 starts to rise. This leads to panting, which isn't efficient on land, but is worse in the water.

I seriously doubt that anyone who has posted in these overexertion threads is working significantly past the anaerobic threshold, simply because people won't tolerate it. Maybe Dan does it, chasing dolphins . . .

 

[Kevrumbo]

Taken from Undersea Biomedical Research, Vol 5, No. 4 December 1978 Hesser, Fagraeus, and Adolfson:


"Studies on the narcotic action of various gases have shown that the ratio of narcotic or anesthetic potency of CO2 and N20 approximates 4:1, and that of N2O and N2 30:1. From these figures it can be calculated that CO2 has at least 120 times the narcotic potency of nitrogen. Our data would suggest that the narcotic potency of CO2 is even greater, i.e., several hundred times as great as that of nitrogen."

Dr. Bookspan is the author of Diving Physiology in Plain English and various medical board review courses for hyperbaric medicine. From Dr. Bookspan's article, supra.


"Carbon dioxide retention is now viewed as a contributor to oxygen toxicity and nitrogen narcosis, suspected as a contributor to decompression sickness, and implicated in incidents of underwater confusion and loss of consciousness."

"Hypoxic Drive and the Intern Error" and other esoteric clinical pathologies aside, the issue here is to break the vicious & building cycle of Narcosis and CO2 retention. Abort the dive, ascend properly with your buddy to your safety stop, deploy your SMB as needed, and surface. (Bumping my previous post from before to below):

Deep Air with increased Gas Density & Work-of-Breathing; then throw in Physical Exertion or a Stress Condition, resulting in overbreathing the regulator --all leading to the Vicious Cycle of CO2 Retention and sudden Narcosis. Can result in severe cognitive impairment at depth or worst case stupor and ultimately unconsciousness. . .

 

[dumpsterDiver]

. The whole issue is somewhat contradictory. So many people view diving as a challenge.. see who can use the least air AND maintain perfect, stable buoyancy control. These two objectives can really be the CAUSE of problems and issues like this.

If you want to maintain perfect buoyancy control, then it is much, much easier if you breath shallow... don't inhale too hard and don't exhale to much. If the tidal volume is minimal than the bouyancy swing on each breathing cycle is minimized and it is easier to be stable. Take great big breaths and exhale all the way and you ARE going to be oscillating up and down to some extent. For an open water diver who doesn't view this as a competition, this is not much of a problem. When taking photographs, stalking fish, tying to do precise hovering for some reason, expereinced divers will manipulate their breathing rate and also how deeply they breath. You ca play these games with breathing while diving if you are drifting along and not doing any work. But if you begin to exert yourself, you really do need to change your breathing and begin to inhale and exhale more fully and i think expereinced divers just know this.. you don't want to get behind the 8-ball.. especially when deep.

The other issue is trying to conserve air. Obviously this can result in Carbon Dioxide issues.

As some other people have mentioned, the key is to breath more deeply and when you begin to feel overworked, then you must concentrate on exhaling more fully and of course STOP using your legs.

Scuba spearfisherman must really understand this. They may stop breathing completely and stalk a fish, swimmng a long distance without breathing. Then make a shot, the fish swims away with a shaft and then the diver needs to sprint after the fish at 100% effort to catch it before it disappears. This can be extremely taxing and if you do it on air when deep ,you can get in SERIOUS trouble very quick. If you get out of breath like that, deep below 180 on air.. it is almost better to just come up because you are not going to be able to do much for a long time while you lay there and try to recover.

 

[John C. Ratliff]

Kevrumbo,

You realize that you are quoting a biomedical study that is 35 years old. Here is the abstract of that study:

Undersea Biomed Res. 1978 Dec;5(4):391-400.
[h=1]Roles of nitrogen, oxygen, and carbon dioxide in compressed-air narcosis.[/h]Hesser CM, Fagraeus L, Adolfson J.
[h=3]Abstract[/h]In an attempt to determine the roles of nitrogen, oxygen, and carbon dioxide in compressed-air narcosis, the effects on performance (mental function and manual dexterity) of adding CO2 in various concentrations to the inspired gas under three different conditions were studied in eight healthy male volunteers. The three conditions were: (1) air breathing at 1.3 ATA; (2) oxygen breathing at 1.7 ATA; and (3) air breathing at 8.0 ATA (same inspired O2 pressure as in (2)). By relating performance to the changes induced in end-tidal (alveolar) gas pressures, and comparing the data from the three conditions, we arrived at the following results and conclusions. A rise in O2 pressure to 1.65 ATA, or in N2 pressure to 6.3 ATA at a constant high PO2 level, caused a significant decrement of 10% in mental function but no consistent effect on psychomotor function. A rise in end-tidal PCO2 of 10 mmHg caused an impairment of approximately 10% in both mental and psychomotor functions. The results suggest that, at raised partial pressures, all three gases have narcotic properties, and that the mechanism of CO2 narcosis differs fundamentally from that of N2 and O2 narcosis.
Roles of nitrogen, oxygen, and carbon di... [Undersea Biomed Res. 1978] - PubMed - NCBI

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